Wi-Fi technology operating in accordance with the IEEE802 11a/b/g standard and operating in the 2.4 GHz and 5 GHz frequency bands today holds the best position for very high speed wireless transmissions, especially in a domestic environment.
The transmission of several video streams, particularly high definition between for example, a station or set top box (STB) and several terminals such as computer laptops, television or other devices, requires the use of a high-order modulation to attain the maximum speed allowed by the standard, namely 54 Mbps. The high-order modulations such as the 64-QAM modulation are more demanding in terms of the output power of the power amplifier than the standard modulations. Indeed, the C/N relationship (Carrier to Noise ratio) for a given quality of reception increases with the order of modulation. Moreover, the higher the order of modulation, the weaker the tolerances to nonlinearities and the more significant the back-off of the power amplifier must be. The back-off corresponds to the margin in relation to the output power of a power amplifier defined at 1 dB of compression to ensure a linear operation of the amplifier.
Finally, the OFDM modulation comprising multiple carriers used in the Wi-Fi systems, being of non-constant envelope, is particularly sensitive to the nonlinearities of the power amplifier.
Consequently, taking into account the prior art of power amplifiers, all of these constraints mean that it is currently difficult to be able to emit the maximum power permitted by the various regulations with cost and power consumption constraints compatible with the targeted products.
In particular, in the 5 GHz (5.47 GHz-5.825 GHz) high frequency band, it is permitted to emit up to 30 dBm of EIRP (Equivalent Isotropic Radiated Power) in Europe and up to 35 dBm of EIRP for the United States. When using antennas with moderate directivities of the order of 8-10 dBi and when considering a transmission loss of 2 dB, linear output powers are required, taking into account the back-off greater than 22 dBm. However, with the currently available power amplifiers, it is not possible to obtain a linear output power greater than 18 dBm. Hence, it is interesting to be able to combine two or more amplifiers offering linear output powers of the order of 18 dBm in order to attain the targeted powers.